Paint Mixing Ratio Calculator
Mix paint and additive by a set ratio.
Results update as you type.
How it works
Two-part paints, coatings, and finishes must be mixed in a precise ratio for proper curing and performance, and this calculator finds the amounts. You enter how much base paint you have, and the mixing ratio (base parts to additive parts), and it returns how much additive — hardener, activator, catalyst, or thinner — to add and the total mixture volume. The ratio, printed on the product, tells you the proportion: a 4:1 ratio means four parts base to one part additive, so 1,000 ml of base needs 250 ml of additive for 1,250 ml total. Getting the ratio right is critical for two-part products like epoxy, polyurethane, and automotive paints, where too little hardener leaves the finish soft or tacky and too much can make it brittle or cause other defects — the chemistry depends on the correct proportion. This calculator works for any ratio and any unit (milliliters, ounces, parts) as long as you're consistent. Some paints also add a separate reduction or thinning ratio for spraying, which you can calculate the same way. Always mix thoroughly and only as much as you can use within the product's pot life (working time), since mixed two-part products begin curing immediately. Follow the manufacturer's specific instructions. Enter the base amount and mixing ratio to find the additive amount.
Additive = base amount × (additive parts ÷ base parts)
A mixing ratio like 4:1 means four parts base paint to one part additive. Multiplying the base amount by the ratio of additive parts to base parts gives how much additive to add. Adding it to the base gives the total volume of mixed product.
Source:Mixing ratios
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter base paint amount, ratio — base parts and ratio — additive parts.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Additive to add updates instantly as you type — no button to press.
Frequently asked questions
How do you calculate a paint mixing ratio?
Multiply the base paint amount by the ratio of additive parts to base parts. For a 4:1 ratio (four parts base to one part additive) with 1,000 ml of base, you add 1,000 times one-quarter, or 250 ml of additive, making 1,250 ml total. This keeps the correct proportion for any amount of base.
Why is the mixing ratio so important?
Two-part paints and coatings cure through a chemical reaction that depends on the correct proportion of base to hardener or activator. Too little hardener leaves the finish soft, tacky, or uncured, while too much can make it brittle or cause defects. Following the exact ratio ensures proper curing, durability, and appearance, so precision matters.
What is a base-to-additive ratio like 4:1?
It means four parts of base paint for every one part of additive, such as hardener or activator. The parts can be any consistent unit — milliliters, ounces, or measured parts — as long as you keep them the same. So 4:1 could be 4 cups base to 1 cup additive, or 400 ml to 100 ml; the proportion is what matters.
What is pot life?
Pot life is the working time you have after mixing a two-part product before it begins to harden and becomes unusable. Because the curing reaction starts immediately upon mixing, you should mix only as much as you can apply within the pot life, which varies by product and temperature. Mixing too much wastes material that cures in the container.
Can I use this for thinning or reduction ratios?
Yes. Thinning or reduction ratios work the same way — for example, a 4:1 paint-to-thinner ratio for spraying means adding one part thinner for every four parts paint. Enter your paint amount as the base and the thinner ratio, and the calculator gives the thinner to add. Follow the product's recommended reduction ratio for your application method.